DEV Community: hk7math

SQL Aggregate Product

hk7math — Thu, 24 Dec 2020 17:24:36 +0000

Been left on CodeSignal for a while because I'm lately rushing for a full stack course~ Today's task appears to be simple but the solution is not equally simple. Indeed, I learnt my lesson. In brief, we are required to do an aggregated product in SQL.

It turns out that such fundamental function is not supported in SQL. You may wanna ponder on it a bit. The hint is: simple "useless" math XD

When I look through the top 10 solutions, ALL OF THEM use exactly the same skill:
Here is this famous workaround

SELECT EXP( SUM( LN( field ) ) ) | 0
FROM table

Please suggest below if you come up with some other ways X)

JavaScript CPU Emulator Problem

hk7math — Mon, 07 Dec 2020 16:24:59 +0000

I've picked up CodeSignal again and aim to solve something every day (either challenges or casual problems). Recently, we got a medium challenge from hamlet_m1. It is to emulate a CPU assembly language. (Hope I didn't mix up technical terms).

This time, I'm proud to be one of the JS solvers together with other 8 geeks:

User	Level	Country	Chars
Thomasz	70	USA	290
Giang_P_r	87	Vietnam	437
kov	93	Hungary	480
hk7math	44	Hong Kong	503
danielhong35	86	USA	512
murtaza_m2	43	Romania	921
omar-aguilar	62	Mexico	1367
linh_pv_9x	82	Vietnam	1490
jonathas_s1	24	Brazil	2198

The best solution by thomasz is an awe to me! Not only is it far shorter than all other solutions, but it is also still highly readable (to people like me who like hacky tricks)

Disclaimer: the full solution just for reference, please tell me to delete it if I violated any rule...

cpuEmulator = s => {

    z = 2 ** 32
    r = Array( 43 ).fill( 0 )
    R = x => +x.split`R`[ 1 ]

    for ( d = 0; l = s[ d++ ]; ) {

        [ c, a, b ] = l.split(/[\s,]/)
        o = y => r[ R( a ) ] = ( r[ R( a ) ] + y + z ) % z

        c == 'MOV' ?
            r[ R( b ) ] = R( a ) + 1 ? r[ R( a ) ] : +a  :            
        c == 'ADD' ?
            o( r[ R( b ) ] ) :
        c == 'DEC' ?
            o( -1 ) :
        c == 'INC' ?
            o( 1 ) :
        c == 'INV' ?
            o( ~r[ R( a ) ] * 2 + 1 ) :
        c == 'JMP' || c == 'JZ' && !r[ 0 ] ?
            d = +a - 1 : 0       
    }

    return r[ 42 ] + ''
}

Here are some tricks I discovered in this snippet:

Array(n).fill(x) to initialize an array of length n with prefilled values x (be careful about multi-dimension arrays though)
+'numeric string' to cast a string as a number or NaN
Regex /[xyz]/ to split string by separators x, y, z simultaneously
c == 'case1' ? ... : c == 'case2' ? ... : ... to well format nested ternary operators as a switch-case
number + '' to cast a number as a string

Feel free to drop a comment about your takeaways :D

FB Notes' gone.. here :'/

hk7math — Fri, 20 Nov 2020 18:53:15 +0000

In the good old days, I used FB notes as my diary. It recorded the ups and downs in my youth. That time, I had a crush on a girl and I wrote to her nearly every day. She was the only audience of those notes, but I guessed she never knew because she probably wouldn't click into my wall or profile. Yup, it was an 1-way love.

For 10 years, I kept the habit of writing down my thoughts in occasional notes and setting her to be the single audience. Until one day, she messaged me... She told me about a mid-night notification that someone shared a note ONLY with her... FB changed the rule...

What an embarrassing moment. But this might be a deepest wish in my heart for some day she found that out of her own will... We had some chat and she said she didn't remember much: The months she evaded from me. The dates I confessed to her. The years she let me wait for an answer which never came. After years, I know I don't love her any more. It is merely the imagination I created out of my memory. But the love was real and all recorded on the notes...

Today, I just knew FB removed the Notes... It's like part of me has ended with it. Thank you for reading the story of a geek. If you love someone, I have 3 thoughts to share:

treasure the love
ask for no return
be proud of yourself if you did the above

Lastly, I'm glad my notes are still archived here on FB, hope this link could help someone similar to me but less geek=)

https://fb.com/0/allactivity?category_key=NOTECLUSTER

JavaScript Big Combination Problem

hk7math — Wed, 15 Jan 2020 16:14:15 +0000

A recent CodeSignal Challenge was to calculate 1000C500 (mod 1e9+7) and I got defeated =(

All my trials exceeded the time limit.. Here is the best JS solution by psr
, could anyone explain what happens in this line??? I learnt ES6 but got no idea about this syntax...

f[o = n + 1/k] = o in f

full solution for reference, please tell me to delete this if I violated any rule...

f = countWays = (n, k) => f[o = n + 1/k] = o in f
    ? f[o]
    : k 
        ? n && (f(--n, k) + f(n, k - 1)) % (1e9 + 7)
        : 1